Thin films from relatively high molecular weight aromatic polyimides generally exhibit toughness, flexibility, solvent resistance, high glass transition temperatures (Tg) and thermal stability. In many cases these materials, due to their aromatic structure exhibit good ultraviolet (UV) radiation resistance; however they also display significant color (D. Wilson, H. D. Stenzenberger and P. M. Hergenrother, “Polyimides”, Blackie and Son, Glasgow and London, 1990). Kapton® polyimide film is a good example of the typical amber color exhibited by thin films. No commercially available polyimides are resistant to degradation by atomic oxygen exposure. The preparation of low color polyimides that are UV resistant has been reported (A. K. St. Clair, T. L. St. Clair and W. S. Slemp “Recent Advances in Polyimide Science and Technology, W. Weber and M. Gupta, eds., Society of Plastics Engineers, Poughkeepsie, N.Y. 1987, pp. 16-36; A. K. St. Clair and W. S. Slemp, SAMPE Technical Conference Proceedings, 23, 1991; U.S. Pat. Nos. 4,595,548 and 4,603,061 issued Jun. 17, 1986 and Jul. 29, 1986, respectively to National Aeronautics and Space Administration). However none of these polyimides are resistant to atomic oxygen or oxygen plasma degradation.
Some reports detail the preparation of polyimides which contain phenylphosphine oxide units in the polymer backbone (I. K. Varma, G. M. Fohlen and J. A. Parker, Journal of Macromolecular Science-Chemistry, A19(2), 209 (1983); I. K. Varma and B. S. Rao, Journal of Applied Polymer Science, 28, 2805 (1983); I. K. Varma, G. M. Fohlen and J. A. Parker Journal of Polymer Science, Polymer Chemistry Edition, 28, 2017 (1983); P. M. Hergenrother and S. J. Havens, Journal of Polymer Science, Polymer Chemistry Edition, 27, 1161 (1987); U.S. Pat. No. 5,145,937 issued 1992 to the National Aeronautics and Space Administration). Recent reports show that phosphine oxide containing poly(arylene ether)s exhibit atomic oxygen and oxygen plasma resistance [C. D. Smith, H. F. Webster, A. Gungor, J. P. Wightman and J. E. McGrath, High Performance Polymers, 3(4), 211 (1991); J. W. Connell, J. G. Smith, Jr. and P. M. Hergenrother, Journal of Fire Science, 11, 137 (1993); J. G. Smith, Jr., J. W. Connell and P. M. Hergenrother, Polymer, 35, 2834 (1994)]. This was extended to show that polyimides containing phosphine oxide groups were also atomic oxygen and oxygen plasma resistant [(J. W. Connell, J. G. Smith, Jr. and P. M. Hergenrother, Polymer, 36, 5 (1995); J. W. Connell, J. G. Smith, Jr. and P. M. Hergenrother, Polymer, 36, 13 (1995)]. Other polyimides containing phosphine oxide groups have been reported [J. E. McGrath, H. Grubbs, M. E. Rogers, A. Gungor and W. A. Joseph, SAMPE Technical Conference Proceedings, 23, 119 (1991); J. M. Wescott, T. Toon, L. Kiefer and J. E. McGrath, Polymer Preprints, 33(2), 235 (1992); Y. N. Lin, S. Joardar and J. E. McGrath, Polymer Preprints, 34(1), 515 (1993)]. However, in all of these reports, the polyimides containing phosphine oxide groups exhibited high color that ranged from orange to brown and consequently they exhibited poor optical transparency and relatively high solar absorptivities.
The present invention constitutes new compositions of matter, which exhibit unique and unexpected combinations of properties. It concerns new diamines and dianhydrides that contain phenylphosphine oxide groups and polyimides and copolyimides prepared therefrom. The polymers prepared from these aromatic diamines and aromatic dianhydrides exhibit an unexpected combination of properties that include low color in thin film form (1-2 mils thick), low solar absorptivity, high optical transparency, atomic oxygen resistance, vacuum UV radiation resistance, solubility in organic solvents in the imide form, high Tg, and high thermal stability. These compositions of matter are also useful as adhesives, coatings, films, fibers, foams, moldings, powders, prepregs and composite matrices.